Reference work that contains information on all branches of knowledge or that treats a particular branch of knowledge comprehensively.
It is self-contained and explains subjects in greater detail than a dictionary . It differs from an almanac in that its information is not dated and not from pedagogical texts in its attempt to be easy to consult and to be readily understood by the layperson. Though generally written in the form of many separate articles, encyclopaedias vary greatly in format and content. The prototype of modern encyclopaedias is usually acknowledged to be Ephraim Chambers's Cyclopaedia (1728), and the first modern encyclopaedia was the French Encyclopédie (1751–65). The largest general encyclopaedia in English is the Encyclopædia Britannica.